Systemic Lupus Erythematosus (SLE) is an autoimmune disorder characterized by excessive production of a variety of autoantibodies and a wide range of clinical manifestations. Pathogenesis of SLE is complex and not fully understood. There is however evidence that B and T cells are critical to the development of disease, and that T cell-derived cytokines are involved in the SLE-associated inflammatory response. One such cytokine seems to be interleukin (IL)-21, the latest identified member of the gamma-chain-related cytokine family. IL-21 has an important role in the control of the growth, survival, differentiation, and function of both T and B cells, and excessive production of IL-21 has been associated with the development of multiple immune-mediated diseases. Here we review data supporting the involvement of IL-21 in the pathogenesis of SLE.